Web 2.0 Whiteboard Options

Twiddla

Create public meetings, mark up images and files, easy to use. Does not save images and files in the free version.
http://www.twiddla.com/

Imagination Cubed

Easy to use functions, allows you to save and e-mail the results, plays back as a movie instead of a single completed image.
http://www.imaginationcubed.com/

Skrbl - very slow right now
allows uploading of files and pictures, allows saving, good basic set of tools, allows publishing
http://www.skrbl.com

Virtual White Board
lots of options, but none that are very robust, exports as a csv file.
http://www.virtual-whiteboard.co.uk/home.asp

Dabbleboard
Fully functional tools with options to add pictures and documents. Freehand drawing tool is a pain, it requires one to click it each time a new line is drawn, otherwise it goes to shape recognition. Options to save to Dabbleboard or download to the computer. Great video tutorial.
http://www.dabbleboard.com/

Sneffel (Virtual Paper)
limited tools available, does allow picture upload, no way to save results.
http://www.sneffel.com

Nota
A mash up of several applications on a whiteboard, wiki style, stamp of contributor, date, and time for each addition.
http://notaland.com/